Disk space limitations are extremely important because they affect how much content your sites can host. For example, if you have a large website with thousands of files, you may be consuming a lot of disk space. If you were to run out of disk space, you would be unable to update your site, and your site performance would decrease.
Now, of course, at this point, you could update to another hosting plan; however, the time wasted and the amount of dissatisfied visitors will have already taken its toll. It is very important to choose a web hosting plan that will be able to accommodate your site's disk space needs.